This application relates generally to disc drive actuator assemblies and more particularly to a discrete bearing assembly for an actuator assembly.
Conventional disc drive actuator assemblies may have discrete bearing assemblies. These discrete bearings are typically preloaded with a preload spring or a glued arrangement. Resonant behavior of such bearing systems is not directly monitored or controlled. The resonant behavior of actuator assemblies utilizing these discrete bearing assemblies is usually related to the amount of preload on the bearings.
Other actuator assembly designs utilize a cartridge bearing that includes a separate sleeve. These cartridge bearings typically have their preload set utilizing a dead weight and glue on the cartridge alone. For example, NSK (Nippon Steel K) measures the axial resonant frequency of the cartridge bearing during a push fit operation that sets the preload in the cartridge bearing. This push fit operation does not take into account the radial stiffness of the attachment method to the actuator or the resonance of the whole actuator assembly, however, since it is done on the cartridge alone. In addition, the push fit operation does not take into account resonance of the actuator assembly after it has been fastened to the base plate in the disc drive. Consequently, the radial stiffness and resonance of the whole actuator assembly is simply not addressed. This results in less than predictable actuator assembly resonance performance when the actuator assembly is actually operated and unpredictable performance of the disc drive as a whole. Accordingly, there is a need for a bearing assembly that permits a more predictable resonance behavior when installed in the disc drive.
Against this backdrop the present invention has been developed. One embodiment of the present invention is a method of measuring the vibration of the actuator assembly in the plane of rotation of the actuator assembly and determining the resonance behavior of the actuator assembly from the measured vibrations. This method is superior to the prior art in that it directly determines the resonance behavior in the plane of rotation of the actuator assembly and also determines the resonance behavior of the assembly after it has been fastened to the drive.
Another embodiment of the present invention permits the easy adjustment of the actuator assembly resonance behavior during the manufacturing process without requiring gluing or extra parts and without the error introduced by measuring the resonance behavior before the final assembly of the actuator assembly to the drive. The pivot bearing assembly in accordance with the present invention incorporates an actuator pivot pin that also functions as a preload adjustment screw. The pivot pin has a head portion, a cylindrical shaft portion, and a distal threaded end portion. The pivot bearing assembly includes a pair of discrete bearing assemblies mounted on the cylindrical shaft portion of the pivot pin. Sandwiched between the bearings on the pivot pin is a pivot portion of the actuator arm. Each bearing assembly includes an outer race sleeve and an inner race sleeve concentrically spaced apart by ball bearings. When the two bearing assemblies are placed on the pivot pin with the actuator pivot portion sandwiched therebetween, and the threaded portion of the pin is threaded into the base plate of the disc drive, the head portion of the pin contacts the inner race of the upper bearing. The inner race of the lower bearing contacts the base plate. The outer races of the upper and lower bearing assemblies each contact the pivot portion of the actuator arm. The base plate is formed with a raised shoulder around the threaded bore receiving the threaded portion of the pivot pin. The outer race of the lower bearing is beyond the shoulder and thus does not contact the base plate. The shoulder permits the actuator arm to rotate freely on the bearings in a plane of rotation orthogonal to the pivot pin. Tightening the pivot pin into the base plate places a preload force through the bearing assemblies onto the actuator arm.
A laser measuring device aimed at a benchmark on the actuator arm is used to measure vibration of the actuator arm in the plane of rotation of the actuator arm as the pivot screw is tightened during drive manufacture. Resonance behavior of the actuator assembly in the plane of rotation is determined from the measured vibration. Based on the determined resonance behavior, the pivot screw is further tightened or loosened to adjust the preload on the bearing assemblies to provide optimum resonance performance of the actuator assembly. In this arrangement, the preload is applied during final drive assembly, and thus the preload force can be optimized to account for all sources of resonance vibration from the drive as well as permit adjustment for radial stiffness and actual resonance performance.